Solenoid-operated pressure control valve

Abstract

A hydraulic pressure control valve uses a stepped valve spool having a differential area exposed to supply pressure to provide a small resultant force on the spool. A linear electric solenoid provides a linearly variable force on the valve spool to variably position the spool. In a basic embodiment, the linear solenoid force opposes the resultant supply pressure force to position the spool and control hydraulic outlet pressure. Other embodiments are employed to control brake pressure in a transit car. In a second embodiment, the resultant hydraulic pressure force is opposed by the linear solenoid force to position the spool during normal service braking. Brake pressure is proportioned to car weight by varying current to the linear solenoid. When the transit car emergency brake pipe is dumped, load weigh air pressure and spring forces position the spool in an emergency brake pressure position proportional to car weight. These forces are normally neutralized by emergency brake pipe pressure during service braking. In a third embodiment, the selectively variable linear solenoid force supplements the resultant pressure force to position the valve spool against the force of a spring and load weigh air pressure. This embodiment provides emergency brake pressure proportional to car weight when electric current is cut off to the solenoid.

We claim: 
     
       1. A fluid pressure control valve for controlling brake operators in a transit car which has a pneumatic emergency brake pipe and a pneumatic load weigh device, the valve comprising a body having a stepped bore which has an inlet port connected to a source of pressure fluid, an outlet port connected to the brake operators, and a drain port connected to a hydraulic reservoir,   a stepped spool slidable in the bore having opposed first and second valving lands, the first land having an effective area larger than the area of the second land by a differential area, the spool being movable between a fill position connecting the inlet and outlet ports and a drain position connecting the outlet and drain ports, the lands being exposed to outlet pressure fluid which biases the spool toward drain position by a first force produced by outlet fluid pressure acting on the differential area, and   means for applying a second force to the spool opposing the first force to bias the spool toward fill position, including a selectively variable proportional linear electric device, a pneumatic brake pipe operator responsive to brake pipe pressure, and a load weigh operator responsive to vehicle weight, each independently operable to selectively vary the second force to selectively position the spool.   
     
     
       2. The fluid pressure control valve of claim 1, wherein the electric device is a proportional linear solenoid having an output rod engaging the spool with an opposing solenoid force that is proportional to current input and is substantially constant over the range of rod travel. 
     
     
       3. The fluid pressure control valve of claim 2, wherein the second force means includes a biasing device engaging the output rod to selectively increase the solenoid force. 
     
     
       4. The fluid pressure control valve of claim 3, wherein the biasing device includes a spring for increasing the solenoid force and control means for varying the spring force. 
     
     
       5. The fluid pressure control valve of claim 4, wherein the control means includes the load weigh operator which increases spring force with a load weigh force directly proportional to car weight. 
     
     
       6. The fluid pressure control valve of claim 5, wherein the brake pipe operator responds to the supply of brake pipe pressure to release the spring force and responds to the removal of brake pipe pressure to apply the spring force. 
     
     
       7. The fluid pressure control valve of claim 6, wherein the control means includes a mechanical adjustment for adjusting the spring force. 
     
     
       8. The fluid pressure control valve of claim 7, wherein the load weigh operator is responsive to a load weigh pneumatic pressure indicative of car weight to increase spring pressure in direct proportion to load weigh pneumatic pressure. 
     
     
       9. A fluid pressure control valve for controlling fluid pressure in a hydraulic device, comprising a body having a stepped bore which has an inlet port connected to a source of pressure fluid, an outlet port connected to the hydraulic device, and a drain port connected to a hydraulic reservoir,   a stepped spool slidable in the bore having opposed first and second valving lands, the first land having an effective area larger than the effective area of the second land by a differential area, the spool being movable between a fill position connecting the inlet and outlet ports and a drain position connecting the outlet and drain ports, the lands being exposed to outlet pressure fluid which biases the spool toward drain position by a first force produced by outlet fluid pressure acting on the differential area, and   means for applying a second force to the spool opposing the first force to bias the spool toward fill position including   a biasing device including a spring engaging one end of the spool,   pneumatic pressure responsive means responsive to a supply of pneumatic pressure to increase spring pressure in direct proportion to pneumatic pressure, and   a selectively variable proportional linear solenoid having an output rod engaging the other end of the spool with a variable solenoid force, which is proportional to current input and is substantially constant over the range of rod travel, for selectively varying the second force to selectively position the spool and vary the fluid pressure in the hydraulic device.   
     
     
       10. The fluid pressure control valve of claim 9, wherein the biasing device includes a mechanical adjustment for adjusting the spring force. 
     
     
       11. A fluid pressure control valve for controlling brake operators in a transit car which has a source of pneumatic pressure that varies with car weight, the valve comprising a body having a stepped bore which has an inlet port connected to a source of pressure fluid, an outlet port connected to the brake operators, and a drain port connected to a hydraulic reservoir,   a stepped spool slidable in the bore having opposed first and second valving lands, the first land having an effective area larger than the area of the second land by a differential area, the spool being movable between a fill position connecting the inlet and outlet ports and a drain position connecting the outlet and drain ports, the lands being exposed to outlet pressure fluid which biases the spool toward drain position by a first force produced by outlet fluid pressure acting on the differential area, and   control means for applying a second force to the spool opposing the first force to bias the spool toward fill position, including a spring engaging one end of the spool,   a pneumatic operator connected to the supply of pneumatic pressure and responsive thereto to increase spring pressure in direct proportion to car weight to selectively increase the second force, and   a selectively variable proportional linear electric solenoid, having an output rod engaging the other end of the spool with a variable solenoid force which is proportional to current input and substantially constant over the range of rod travel, wherein the pneumatic operator and solenoid are each independently operable to selectively vary the second force to selectively position the spool.       
     
     
       12. The fluid pressure control valve of claim 11, wherein the control means includes a mechanical adjustment for adjusting the spring force. 
     
     
       13. A fluid pressure control valve for variably controlling the supply of pressure fluid to brake operators which operate the brakes in a transit car that has signalling means for signalling transit car conditions, one of which is an emergency condition, the valve comprising a body having a stepped bore which has an inlet port connected to a source of pressure fluid, an outlet port connected to the brake operators, and a drain port connected to a hydraulic reservoir,   a stepped spool slidable in the bore having opposed first and second valving lands, the first land having an effective area larger than the area of the second land by a differential area, the spool being movable between a plurality of fill positions connecting the inlet and outlet ports and a drain position connecting the outlet and drain ports, the lands being exposed to outlet pressure fluid which biases the spool toward drain position by a first force produced by outlet fluid pressure acting on the differential area,   control means for applying a variable second force to the spool which opposes the first force to bias the spool toward the fill positions, including a selectively variable proportional linear electric device and biasing means which produce forces that combine to provide the variable second force to move the spool to the plurality of fill positions, thus supplying pressure fluid at variable pressures to the brakes to provide a plurality of braking rates, and   emergency means for maximizing the second force to move the spool to a fill position that supplies pressure fluid to the brakes to provide an emergency braking rate.   
     
     
       14. The fluid pressure control valve of claim 13, wherein the selectively variable proportional linear electric device is a proportional linear solenoid having an output rod engaging the spool with a force proportional to current input that is substantially constant throughout output rod travel, the solenoid output force variably opposing the biasing means force to provide the variable second force. 
     
     
       15. The fluid pressure control valve of claim 14, wherein the solenoid output force opposes the biasing force to produce the second force and the emergency means comprises signals received from the signalling means for halting current input to the solenoid to maximize the second force to supply pressure fluid to the brakes to provide the emergency braking rate. 
     
     
       16. The fluid pressure control valve of claim 13 wherein the transit car signalling means include load weigh means for signalling transit car weight, further including force adjustment means responsive to car weight signals received from the load weigh means to vary the second force and the supply of pressure fluid to the vehicle brakes in accordance with vehicle weight to produce a selected braking rate despite variations in transit car weight. 
     
     
       17. The fluid pressure control valve of claim 16, wherein the load weigh means include a source of pneumatic pressure which varies with car weight, the control means include a pneumatic operator connected to the supply of pneumatic pressure and responsive thereto to increase the second force in direct proportion to pneumatic pressure. 
     
     
       18. The pressure control valve of claim 13, wherein the signalling means comprise a pneumatic brake pipe having a pressure, and the emergency means comprise means for applying a variable spring force to the spool to move the spool to a fill position that supplies pressure fluid to the brakes to provide the emergency braking rate, and an operator responsive to brake pipe pressure, wherein the brake pipe operator responds to the removal of brake pipe pressure to apply the spring force, and responds to supply of brake pipe pressure to remove the spring force. 
     
     
       19. The fluid pressure control valve of claim 18, wherein the control means include a mechanical adjustment for adjusting the biasing means to selectively vary the second force. 
     
     
       20. The fluid pressure control valve of claim 13, wherein the biasing means includes a spring applying a spring force to one end of the spool and the control means include a mechanical adjustment for adjusting the spring to selectively vary the second force. 
     
     
       21. The fluid pressure control valve of claim 20, wherein the electric device is a proportional linear solenoid having an output rod engaging the other end of the spool with a variable solenoid force, the solenoid force being proportional to current input and substantially constant over the range of rod travel. 
     
     
       22. The fluid pressure control valve of claim 20, wherein the transit car signalling means include a pneumatic operator connected to a supply of pneumatic pressure and responsive thereto to increase the spring force on the spool in direct proportion to pneumatic pressure. 
     
     
       23. The fluid pressure control valve of claim 22, wherein the pneumatic pressure varies with transit car weight to vary spring force and vary spool position to produce a selected braking rate despite variations in transit car weight.